Reduction of electrolytic cell voltage by anode vibration

ABSTRACT

The operating voltage of an electrolytic cell in which gaseous evolution occurs at the anode is reduced by applying high speed mechanical vibration to the anode.

llnited States Patent [1 1 Carlson 1 Oct. 23, 1973 [54] REDUCTION OFELECTROLYTIC CELL 2,919,235 12/1959 Roller 204/273 VOLTAGE BY ANODEVIBRATION FORElGN PATENTS OR APPLICATIONS [75] Inventor: Richard C.Carlson, Euclid, Ohio 1,284,288 10/1970 U.S.S.R 204/273 [7 Assignee:Diamond a k Corporation 1,111,392 2/1956 France 204/99 Cleveland, OhioOTHER PUBLICATIONS [22] Filed: 4 1971 Modern Electroplating byLowenheim, 2nd Ed., 1963,

pages 18-19. [21] Appl. No.1 186,082

Primary Examiner-H0ward S. Williams 52 us. Cl 204/98, 204/128, 204/129,Andrews Attorney-R0y Dav1s et al.

[51] Int. Cl C0lb 7/06 58 Field of Search... 204/261, 273, 98, [57]ABSTRACT 204/128, 162 S, 163 S, 129 The operating voltage of anelectrolytic cell in which gaseous evolution occurs at the anode isreduced by [56] References Cited a lyin high s eed mechanical vibrationto the an- 7 PP g P UNITED STATES PATENTS 3,580,833 5/1971 Cooper 204/992 Claims, 1 Drawing Figure VOLTAGE PATENTED 0B! 23 W73 BY v R y UINVENTOR RICHARD C. CARLSON ATTORNEY REDUCTION OF ELECTROLYTIC CELLVOLTAGE BY ANODIE VIBRATION BACKGROUND OF THE INVENTION A variety ofelectrochemical reactions is known wherein electrical current is passedthrough an aqueous electrolyte between an anode and an opposed cathode,the current being such as to result in the generation of a gas or gassesat the anodic surface. Electrowinning of metals from aqueous solution,the electrolysis of water and the production of chlorine, caustic andthe chemical compounds thereof are but a few examples of such reactions.As the applied anode current density in these processes is increased,the rate of production and the amount of gaseous evolution increase, asdoes the operating cell voltage. At least initially, this increase involtage is, for all practical purposes, in direct relation to theincrease incurrent density. However, it has been noted at the highercurrent densities desirable in order to increase the production rate ofa given electrolytic cell that the voltage begins to increase at a rategreater than theoretical, resulting in an increase in power consumptionper unit of product.

Attempts have been made to counteract this undesirable rate of increasein voltage. For example, following the suggestion of certain prior art,the electrolyte has been subjected to ultrasonic vibrations with,unfortunately, no detectable effect.

STATEMENT OF THE INVENTION Therefore it is an object of the presentinvention to I provide a method for reducing the operating voltage ofrate of production is such that considerable quantities of gas areevolved and rapid decomposition of the electrolyte occurs at the anodicsurface. These conditions of high current density have becomeincreasingly common-place in recent years with the advent ofdimensionally stable anodes that are not subject to the usualdecomposition and attrition of, for example, graphite at increasedcurrent densities.

The action to which the anode is subjected is stated as being high speedmechanical vibration. As suggested by this phrase, together with theword directly, it is intended that the anode itself, especially theworking face thereof, be caused to vibrate, preferaaqueous electrolytebetween an anode and an opposed DESCRIPTION OF THE DRAWING The FIGURE isa graph illustrating the improved performance of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, theinvention is applicable to those electrochemical reactions wherein anelectric current is passed through an aqueous electrolyte at a voltagesufficient to achieve the desired reaction and result in the evolutionof a gas or gasses at the anodic surface. Generally the gas evolvedeither is desired product (e.g., chlorine) or is required for asubsequent chemical reaction resulting in the desired product (e.g.,chlorine reacting to chlorate). However, the invention functions equallyas well where the gas evolved is an unavoidable by-product, the desiredreaction occurring predominantly at the cathodic surface (e.g., oxygenat the anode in electrowinning).

The advantage of the instant invention is most marked at relatively highcurrent densities wherein the bly at a rate in excess of 6,000,especially in excess of 9,000 vibrations per minute and up to speedswhich may be considered ultrasonic (e.g., 20,000 vibrations/- second).The vibrations are applied directly to the anode and/or its supportingand connecting framework up to and including the current lead in(busbar). Vibrations applied to other of the cell components, such asthe cell supports or sidewalls, or to the electrolyte have been found tohave substantially no effect.

The means for inducing the mechanical vibration is of little or noconsequence to the invention, although obviously important from apractical standpoint. It has been found that in order to be effectivethe vibrations must be continually applied, that is, upon cessation ofthe vibrations the operating voltage immediately increases to its prior,excessive, value. For this reason the vibrating means should be chosenfor its durability and simplicity of operation and maintenance. Typicalof such are those vibrators in which compressed air is used to impartunbalanced rotation to balls or rollers which in turn induce vibrationsin members in contact therewith.

Illustrative of the present invention is its effect upon theelectrolysis of an aqueous alkali metal halide solution in a cellemploying a dimensionally stable anode and a flowing mercury cathode.The cell used is a horizontal-type mercury cell employing an anodesuspended above a steel cathode base plate, the assembly being enclosedto contain the electrolyte and products of electrolysis. Thedimensionally stable anode is constructed primarily of titanium, issupported by an anode frame and is connected to a copper busbar. Ananode riser leads from the busbar connection to the interior of thecell, the active working face of the anode consisting of a plurality ofelongated rod-like elements positioned in a plane parallel to theflowing mercury surface and connected by welding through secondaryconductors to the anode riser. The surface of these titanium rods iscoated with an electrically-conductive electrocatalytically activematerial, in this case a titanium dioxide-ruthenium oxide deposit. Theanodecathode gap is established at 0.136 inch. A 305 grams/- litersodium chloride solution is employed as the electrolyte at an averagecell temperature of 76C.

The Figure shows the relationship between applied anode current densityand the operating cell voltage at the above-described conditions. Thefirst line (1) charts the theoretical straight line relationship betweenvoltage and current density for the given conditions. Line 3 is a plotof the anode current density versus the actual cell voltage obtained,measured from anode face to mercury. Line 2 is again a plot of themeasured voltage at the various current densities, all conditions beingthe same as those of Line 3 with the exception that mechanical vibrationis employed.

Vibration is effected by placing a commerciallyavailable compressedair-driven vibrator (Vibrolator Model BDR-l6, Martin Engineering Co.)directly on the anode busbar. The vibrator operates within the range of9,000-1 1,000 vibrations per minute. The location of the vibrator on thecopper busbar is a matter of convenience, attachment to the anode per seand the anode frame having been found to give equivalent results.

The substantial reduction in voltage obtained by the application ofvibrational force is readily seen from the attached figure, reductionsof up to 300 millivolts having been observed.

While the invention has been described with reference to certainpreferred embodiments thereof, it is not to be so limited since changesand alterations may be made therein while remaining within the scope ofthe appended claims.

I claim:

1. An improvement in the method of electrolyzing alkali metal halidesolutions by passing a current between an anode and an opposed cathode,said current being sufficient to cause gaseous evolution at the anode,which improvement consists essentially of causing said anode to vibraterapidly and continuously by the direct application of mechanical forceto the anode structure.

2. In a method of electrolyzing an aqueous alkali metal halide bypassing current through said aqueous halide between an anode and anopposed cathode at an anode current density of greater than 8 amperesper square inch, the improvement which consists essentially of reducingthe operating voltage by causing said anode to vibrate continuously at arate of from 6,000 vibrations per minute up to ultrasonic by the directapplication of mechanical force to the anode structure.

2. In a method of electrolyzing an aqueous alkali metal halide bypassing current through said aqueous halide between an anode and anopposed cathode at an anode current density of greater than 8 amperesper square inch, the improvement which consists essentially of reducingthe operating voltage by causing said anode to vibrate continuously at arate of from 6,000 vibrations per minute up to ultrasonic by the directapplication of mechanical force to the anode structure.